Spatial orientations of common bean influence the activities and population dynamics of bean stem maggot (Ophiomyia phaseoli) and bean foliage beetle (Ootheca mutabilis)

Abstract

Bean stem maggot (BSM) (Ophiomyia phaseoli) and bean foliage beetle (BFB) (Ootheca mutabilis) pose a serious challenge to production. Many practices have been employed to manage these pests. However, little or no emphasis has been on basic agronomic practices such as plant spacing as a tool for pest management of BSM and BFB. In the present study, the role of plant orientation (plant spacing) on the activities and population dynamics of BSM and BFB was examined in a pesticide-free field trial in Bamenda, Cameroon. Different plant orientations namely 15 cm x 15 cm (442500 plants ha^-1), 20 cm  x 20 cm (250000 plants ha^-1), 30 cm x 30 cm (110000 plants ha^-1) and 40 cm x 40 cm (62500 plants ha^-1) were test in a randomized complete block design with 4 replicates. Data was collected on oviposition holes on leaves of common bean by BSM, BSM population dynamics, leaf damage score by BFB, and population dynamics of BFB. The number of oviposition holes, the mean cumulative number of BSM, the mean leaf damage scores and the mean cumulative number of BFB were significantly higher (p<0.05) in dense plots (15 cm x 15 cm) than in the other plots. The activity of BSM and BFM increased over time. The principal component analysis revealed that the first two components accounted for 99.17% of the variation. Linear discriminant analysis with Mahalanobus distances with an 87.5% cross-validation by Jacknife procedure revealed that spatial orientation of 20 cm x 20 cm and 30 cm x 30 cm were very similar and significantly (p<0.001) different from the others. For pest management purposes, plant orientations of 20 cm x 20 cm and 30 cm 30 cm can be recommended since they recorded low BSM and BFB activity. For future perspective, it is important assess the effect of different plant orientation on yield and pest parameters concurrently.